1. Field of the Invention
The present invention relates to a call admission control device and a call admission control method, and more specifically to a call admission control device and a call admission control method for controlling the admission of a call in a packet communication system in mobile communications.
2. Description of the Related Art
A mobile telephone communication system performs a communication using finite resources (frequencies and power), and the upper limit is applied to the communication capacity. Therefore, it is necessary to limit the number of mobile terminals in a cell depending on the communication capacity. Practically, when a new mobile station starts communications in the cell, it is necessary to judge whether or not the new mobile station can start a communication in the cell. The control is referred to as call admission control. The status in which a new mobile station cannot start a communication in the cell, that is, the status in which the communication capacity is being used substantially 100%, is referred to as a capacity limit.
The conventional method call admission control is a control method of, for example, allowing a new mobile station to start communications when the total number of mobile stations being communicating in the cell does not exceed a predetermined threshold value, and not allowing a new mobile station to start communications when the total number of mobile stations being communicating in the cell exceeds the predetermined threshold value.
Relating to the standardization of a third generation mobile communication system, what is called IMT-2000, the standard specifications related to the W-CDMA system and the CDMA 2000 system are prescribed respectively for the 3GPP (third-generation partnership project) and 3GPP2 (third-generation partnership project 2).
In the 3GPP, with the recent fast spread of the Internet, based on the prediction that high speed and large capacitance traffic by the download, etc. from a database and a Web site especially in the downlink, the specification of the “HSDPA (High Speed Downlink Packet Access)” as a high speed packet transmission system in the downlink direction is prescribed (for example, refer to 3GPP TR25.848v4.0.0).
As for the 3GPP2, from a similar point of view, the specification of the “1×−EVDO” as a high speed dedicated transmission system in the downlink direction is prescribed (for example, refer to 3GPP2 C.S0024Rev.1.0.0). In the CDMA 2000 1×EV-DO, the DO means “Data Only”.
Described below is the priority classes in the above-mentioned HSDPA.
In the HSDPA, it is possible to set a plurality of priority classes to transmit packet data having various QoS (Quality of Service). For example, there can be a method of transmitting a packet by setting the packet data of a mobile station for performing VoIP as a first priority class, setting the packet of a mobile station for performing download by an FTP (File Transfer Protocol) as a second priority class, and transmitting the packet data of a mobile station for performing VoIP of high QoS in time on a priority basis. Otherwise, there can be a method of transmitting a packet by setting the packet data of a mobile station in a contract of a high class as the type of contract as a first priority class, setting the packet data of a mobile station in a contract of a low class as the type of contract as a second priority class, and transmitting all packet data of mobile stations in a contract of a high class and then transmitting the packet data of a mobile station in a contract of a low class.
JP2004-328157A (hereinafter refer to as the patent document 1) describes the technique of possibly allocating a call depending on the priority and enhancing the use efficiency of shared resources by determining the influence of a call of a low priority on a system when the call of the low priority is detected in the call admission control device for allocating necessary resources among the shared resources to communications of a plurality of calls of different priorities, and determining the admission of the call of a low priority based on the determination result. JP2002-223239A (hereinafter refer to as the patent document 2) describes the technique of regulating the admission of a new call depending on the type of service or the priority.